fix #719 Filter the empty buffers emitted by the Publisher

[violetagg]

Mark the promise as successful and do not proceed with writing.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (0.8.x@b15da7d). Click here to learn what that means.
The diff coverage is 50%.

@@           Coverage Diff            @@
##             0.8.x     #720   +/-   ##
========================================
  Coverage         ?   65.73%           
  Complexity       ?     1402           
========================================
  Files            ?      130           
  Lines            ?     6628           
  Branches         ?      891           
========================================
  Hits             ?     4357           
  Misses           ?     1776           
  Partials         ?      495

Impacted Files	Coverage Δ	Complexity Δ
...eactor/netty/channel/ChannelOperationsHandler.java	70.86% <50%> (ø)	66 <0> (?)

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[smaldini]

Superseeded by #725

[smaldini]

Since channeloperationshandler is rewritten in #725 we have ported the tests and fixes here